Senior Democrats on Capitol Hill are calling for a congressional investigation into the justice department’s handling of an ongoing inquiry into Deutsche Bank, saying that Donald Trump had conflicts of interest with the German bank, his biggest creditor.

Maxine Waters, the top Democrat on the House financial services committee, urged her Republican colleagues to launch their own investigation into the nature of Deutsche Bank’s money-laundering scheme, who participated in the arrangement and whether it involved any other violations of US law beyond the failure to maintain anti-money laundering controls.

Deutsche Bank has already been ordered to pay more than $800m (£660m) in fines in the US and UK for failing to stop the improper and corrupt transfer of more than $10bn out of Russia. It is also being investigated by the justice department (DoJ).

The Guardian reported last month that the German bank undertook a close examination of the president’s personal bank account and those held by his family, in order to ascertain whether they had any suspicious links to Russia. None were found.

According to an analysis by Bloomberg, Trump now owes Deutsche about $300m. He has four large mortgages, all issued by Deutsche’s private bank.

Waters said in a letter to Jeb Hensarling, the chairman of the House financial services committee, that she was concerned “about the integrity of this criminal probe” given Trump’s “conflicts of interest” and the “suspicious ties” between Trump’s inner circle and the Russian government.

She cited the testimony of Jeff Sessions, the US attorney general, who swore under oath during his confirmation hearing that he had never had any contact with Russian officials during the presidential campaign, even though it was subsequently revealed that he had two meetings with the Russian ambassador to the US, Sergey Kislyak.

Sessions has recused himself from the DoJ’s investigation into allegations that Russia meddled in the US election, possibly with the help of Trump campaign officials. The department’s investigation into Deutsche Bank, however, still appears to be under Sessions’s purview.

Waters said the Trump administration’s “extensive ties” to Russian government officials and oligarchs raised serious concerns about whether the president and his inner circle would direct the DoJ to steer clear of issues that could implicate those who benefited from the Deutsche Bank scheme.

The alleged ties between Russia and a top administration official were also the subject of another letter on Friday. Cory Booker, a Democratic senator from New Jersey, and four other Democrats, sent a letter to Wilbur Ross, the newly confirmed commerce secretary, demanding more information about his role as vice-chair of the Bank of Cyprus.

Ross, a billionaire investor who has claimed in a private conversation with another senator, Bill Nelson, that the White House is “sitting on” his responses, has not replied to two other letters sent by senators before his confimation hearing.

Booker and others, who said they wanted a response from Ross by 24 March, are seeking more information about whether anyone affiliated with the Trump campaign or Trump Organization received direct or indirect loans from the Bank of Cyprus and whether the bank sought to influence the 2016 presidential election.

The senators wanted more information about Ross’s relationship with three Russian officials who were and may still be investors in the bank: Vladimir Strzhalkovsky, Dmitry Rybolovlev and Viktor Vekselberg. It also wanted more information about Ross’s relationship to Josef Ackermann, the former chief executive of Deutsche Bank who was installed as chairman of Bank of Cyprus after Ross was part of a consortium that invested $1bn in the bank in 2014.

Among other questions, the senators wanted to know whether Ross had ever met the Russian ambassador or any other Russian government officials; ever met Russian investors at Mar-a-Lago, Trump’s Florida golf club, and whether the bank was involved with any individuals placed under US sanctions following Russia’s annexation of Crimea.